title: Mannan-binding lectin directly interacts with Toll-like receptor 4 and suppresses lipopolysaccharide-induced inflammatory cytokine secretion from THP-1 cells.
abstract: Mannan-binding lectin (MBL) plays a key role in the lectin pathway of complement activation and can influence cytokine expression. Toll-like receptor 4 (TLR4) is expressed extensively and has been demonstrated to be involved in lipopolysaccharide (LPS)-induced signaling. We first sought to determine whether MBL exposure could modulate LPS-induced inflammatory cytokine secretion and nuclear factor-κB (NF-κB) activity by using the monocytoid cell line THP-1. We then investigated the possible mechanisms underlying any observed regulatory effect. Using ELISA and reverse transcriptase polymerase chain reaction (RT-PCR) analysis, we found that at both the protein and mRNA levels, treatment with MBL suppresses LPS-induced tumor-necrosis factor (TNF)-α and IL-12 production in THP-1 cells. An electrophoretic mobility shift assay and western blot analysis revealed that MBL treatment can inhibit LPS-induced NF-κB DNA binding and translocation in THP-1 cells. While the binding of MBL to THP-1 cells was evident at physiological calcium concentrations, this binding occurred optimally in response to supraphysiological calcium concentrations. This binding can be partly inhibited by treatment with either a soluble form of recombinant TLR4 extracellular domain or anti-TLR4 monoclonal antibody (HTA125). Activation of THP-1 cells by LPS treatment resulted in increased MBL binding. We also observed that MBL could directly bind to the extracellular domain of TLR4 in a dose-dependent manner, and this interaction could attenuate the binding of LPS to cell surfaces. Taken together, these data suggest that MBL may affect cytokine expression through modulation of LPS-/TLR-signaling pathways. These findings suggest that MBL may play an important role in both immune regulation and the signaling pathways involved in cytokine networks.
authors.affiliation: Department of Immunology, Southern Medical University, Guangzhou, China.
authors.forename: Mingyong
authors.initials: M
authors.lastname: Wang
authors.forename: Yue
authors.initials: Y
authors.lastname: Chen
authors.forename: Yani
authors.initials: Y
authors.lastname: Zhang
authors.forename: Liyun
authors.initials: L
authors.lastname: Zhang
authors.forename: Xiao
authors.initials: X
authors.lastname: Lu
authors.forename: Zhengliang
authors.initials: Z
authors.lastname: Chen
mesh_terms: D019138:Antibodies, Blocking / Q000494:pharmacology; D002461:Cell Line, Transformed; D016207:Cytokines / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D018836:Inflammation Mediators / Q000276:immunology / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000276:immunology / Q000378:metabolism; D037601:Mannose-Binding Lectin / Q000276:immunology / Q000378:metabolism*; D009000:Monocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism*; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000276:immunology / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: D019138:Antibodies, Blocking; D016207:Cytokines; D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D037601:Mannose-Binding Lectin; D016328:NF-kappa B; D051197:Toll-Like Receptor 4